Fix English doc of the activation OPs, such as exp, rsqrt, abs....... (#25258)

python/paddle/fluid/layers/layer_function_generator.py

@@ -281,14 +281,16 @@ def generate_activation_fn(op_type):
 
 Return type
   Variable
+
 Examples:
     .. code-block:: python
 
+        import paddle
         import paddle.fluid as fluid
         import numpy as np
 
         inputs = fluid.data(name="x", shape = [None, 4], dtype='float32')
-        output = fluid.layers.%s(inputs)
+        output = paddle.%s(inputs)
 
         exe = fluid.Executor(fluid.CPUPlace())
         exe.run(fluid.default_startup_program())
@@ -297,7 +299,14 @@ Examples:
         img = np.array([[1.0, 2.0, 3.0, 4.0]]).astype(np.float32)
         res = exe.run(fluid.default_main_program(), feed={'x':img}, fetch_list=[output])
         print(res)
-""" % op_type
+
+        # using dygraph
+        with paddle.imperative.guard():
+            dygraph_input = paddle.imperative.to_variable(img)
+            dygraph_output = paddle.%s(dygraph_input)
+            print(dygraph_output.numpy())
+""" % (op_type, op_type)
+
     return func